Histone acetylation: plants and fungi as model systems for the investigation of histone deacetylases

The basic dement of chromatin is the nucleosome. Histones H4, H3, H2A and H 2B form the core histone octamer by protein-protein interactions of their f olded domains. The free, flexible N-terminal extensions of the histones pro trude from the nuclesome; they contain conserved lysines undergoing posttra nslational acetylation. Histone acetyltransferases (HATs) transfer the acet yl moiety of acetyl-coenzyme A to the E-amino group; this reaction is rever ted by histone deacetylases (HDACs). The dynamic equilibrium of the acetyla tion/deacetylation reaction varies throughout the genome; some regions in c hromatin undergo rapid acetylation/deacetylation, whereas others are fixed in a certain acetylation state without significant changes. In general, chr omatin regions engaged in transcription display dynamic acetylation, i.e. H ATs and HDACs are recruited to these regions. Higher plants and fungi have considerably contributed to the unraveling of the multiplicity of HDACs; in particular, plants possess HDACs that have so far not been identified in a nimal cells.